1. Technical Field
This invention relates to armored electric cords and particularly to telephone armored cords that connect telephone handsets to housings of public telephones.
2. Description of the Prior Art
Many public telephones are located in unattended and isolated areas so as to provide reasonable and continuous access for the general public to the telephone system. Vandalism of these public telephones is a problem, however, with the handset and cord being the most vulnerable. Out-of-service conditions may result from damage sustained by the cord due to pulling and stretching of the outer protective covering when subjected to an unusually large force.
Handset cords in public telephones have traditionally been protected by armoring the cord with helically wound metal having adjacent interlocking helices, similar to "BX" or "Greenfield" armor. Unfortunately, these cords when made very strong are also very stiff. Thus, they tend to pull on the hand of the customer holding the handset, thereby adding substantially to its apparent weight.
In an effort to overcome the stiffness problem, an arrangement disclosed in U.S. Pat. No. 3,290,429, issued to R. E. Prescott et al. on Dec. 6, 1966, shows a flexible armored cord for connecting a telephone handset to a telephone housing. The cord comprises a number of separate sleeve-like armored elements forming an armored electric line for a central conductor by surrounding the conductor at longitudinal distributed points. Elements in the cord having inwardly flanged sleeves interlink with smaller diameter elements having outwardly flanged sleeves that extend between the larger inwardly flanged sleeves. This arrangement thus allows the cord to drape loosely and turn about comparatively small radii.
While the Prescott et al. arrangement enhances flexibility, it is nevertheless desirable to provide a simple and inexpensive armored cord which not only secures the handset to the housing with the desired flexibility but also with an increased longitudinal tensile strength to avoid damage that might result in an out-of-service condition.